Field of the Invention
The present invention relates to a broadcasting system for a wireless network. More particularly, the present invention relates to a broadcasting system for a wireless network which is capable of providing broadcast services to mobile terminals with high efficiency.
Description of the Related Art
Provision of broadcast services over a wireless network is a usage type of the wireless network. A typical example of broadcast services may be disaster broadcast, through which emergency announcements such as a special weather report are transmitted to mobile terminals. As another example of broadcast services, a broadcast signal warning of danger may be sent to only telephones located in an area where a landslide is expected, such that people in the area prepare for any accidents. A disaster broadcast service called Multimedia Broadcast Multicast Services (MBMS) is used in an LTE wireless network. For usage of MBMS, refer to non-patent documents 1 and 2.
The broadcast service, which is contrasted with unicast for one-to-one communication, may be construed as representing a one-to-many relationship.
In a broadcasting system using a wireless network, a service is generally broadcast repeatedly with high transmission power for a long time such that the announcement is delivered to all subscribers in case that the quality of the network is bad. For example, when there is an urgent danger such as an urgent disaster, broadcasting may be performed on the assumption of a situation in which the quality of the network is bad (due to, for example, lots of noises). Thereby, many people may receive the broadcast signal. However, unnecessary power consumption occurs, and a long transmission time is taken. Thereby, radio resources may be wasted. Similarly, if broadcasting is performed based on estimation alone without taking transmission factors into account, an announcement may not be delivered to many users, and unnecessary power consumption and waste of radio resources may be caused.